See that fella over there? He's 20 years old. In 10 years, he's got a chance to be a star. Now that fella over there, he's 20 years old, too. In 10 years he's got a chance to be 30.
- Casey Stengel

Live as long as you may. The first twenty years are the longest half of your life.
- Robert Southey

At 20, everything is possible and tomorrow looks friendly.
- Jim Bishop

At 20 years of age the will reigns; at 30 the wit; and at 40 the judgment.
- Ben Franklin